1. Field of the Invention
The present invention relates to a perimeter for examining the visual field of an eye of a client to be examined in an ophthalmic hospital or in an optometrist's office.
2. Related Background Art
A visual field means a range of vision when an eye is directed in a predetermined direction. An examination of visual field is very important not only for diagnosing diseases of the eye but also when looking for symptoms of a wide variety of diseases, such as one causing intracranial abnormalities. Conventionally, an apparatus for examining a visual field (i.e., a perimeter) displays a semi-spherical dome in front of the eye to be examined, and an index is projected on the dome. The client then makes subjective judgements about the index, thus performing self-measurement of the visual field. If the client's eye shows anomalous refraction, a diopter correction lens corresponding to a certain refracting power is inserted in a lens frame arranged in front of the eye. However, it is difficult to find a lens perfectly suited for an eye being examined and to accurately examine the visual field because of distortion in index image light near the lens, eclipse of the index image light by a lens frame, an out-of-focus state of the index image light from the lens, and the like.
In the conventional apparatus, a client under examination observes the index in the semi-spherical dome with one eye per each time. In this case, however, since visual field measurement must be performed while shielding the eye not under examination with an eye-shielding member (e.g., an eye-mask), changing the eye-shielding member from side-to-side is cumbersome, and the client is subjected to the examination in an unnatural state, i.e., with one eye closed.